Detection and quantification of analytes are of prime interest in medical, biochemical, analytical chemical, occupational safety, microelectronic, environmental, military, and forensic applications. Optical sensing and probing is an alternative to electrochemical sensors, which consume analytes, have long response times, have limitations for in vivo use, and are susceptible to poisoning by various contaminants. Various studies on optical methods of analyte detection have been reported in which a dye is immobilized in an analyte-permeable layer. In particular, these studies include sensors whose photoluminescence ("PL") is affected by the analyte. Such affects may include a change in the PL intensity, spectrum, decay time, or polarization.
Commercially available optical sensors typically employ inorganic single crystal III-V compound LEDs as the light source. However, the need to incorporate optical components to convey light to the sensor and to collect the PL for readout increases complexity, size, and costs. Single crystal GaN-based inorganic LEDs also are incompatible with silicon technology, and thus do not permit fabrication of integrated multisensor arrays.
U.S. Pat. No. 5,517,313 relates to an optical sensor using a P-N junction as a light emitting diode. The LED is placed in an indicator layer which is analyte permeable and contains indicator molecules. The presence of analyte alters the amount of light emitted from the indicator molecules. The emitted light is incident upon a photodetector. The amount of current from the photodetector depends upon the incident light, which is used to detect the analyte. U.S. Pat. No. 5,894,351 relates to an optical sensing device which includes a light-emitting P-N junction having a hole in a direction perpendicular to the P-N junction plane. Upon application of an electrical potential across the junction, light is emitted from the junction into the hole. The hole contains an analyte-permeable fluorescent matrix. A photodetector at one end of the hole generates an electrical signal responsive to light emitted by the fluorescent matrix. P-N junction LEDs, however, are typically prepared from materials that are not compatible with existing silicon technologies and thus do not permit fabrication of integrated multisensor arrays. In addition, P-N junction LEDs cannot be made transparent to allow compact and simple sensor devices that utilize "back detection" to collect the PL signal. Further, P-N junction LEDs are fabricated at temperatures that are too high for integration with temperature-sensitive organic and biochemical sensor materials.
Various multicolor thin film electroluminescent ("EL") devices are known in the art. For, example, U.S. Pat. Nos. 4,356,429, 4,539,507, 4,720,432, 4,769,292, 4,885,211, and 5,703,436 and European Patents 92311760.0 and 93107241.7 relate to organic electroluminescent devices ("OLED"). Thin film electroluminescent devices ("TFELD"), such as the OLEDs mentioned above and in, e.g., U.S. Pat. Nos. 5,352,906, 5,821,690, 5,399,502, and 5,807,627, have been known for use in display applications. However, to date no disclosure exists relating to the use of TFELDs to activate optical sensors or probes, much less any recognition of the surprising advantages which the present inventors have achieved by the use of TFELDs in new optical sensing and probing technologies.